Media detector with simplified structure

Abstract: A media detector detects flat media (1) travelling on a transport path formed by a pair of media guides (2,3). Light emitted from a light-emitting element (5a,5b) enters the first media guide (2), is reflected within the first media guide, crosses the media transport path between the media guides, is reflected within the second media guide (3), and exits from the second media guide to a light-sensing element (6a,6b), which converts the light to an electrical signal. The light-emitting and light-sensing elements can be mounted, together with their associated electronics, on a single printed circuit board (11) disposed adjacent to the two media guides (2,3), so that no interconnecting cables are necessary.

Description: BACKGROUND OF THE INVENTION This invention relates to a media detector for use in an automatic teller machine, vending machine, scanner, copier, or other machine that must handle money, paper, plastic cards, or similar flat media. Such a machine typically has a pair of flat media guides separated by a small gap, forming a path through which media are transported by rollers. To monitor the passage of media on this transport path, the machine has a media detector comprising, for example, a light-emitting diode mounted above the upper media guide and a photodiode mounted below the lower media guide. The optic axes of these diodes are aligned with each other and with holes in the media guides, so that normally a beam of light emitted by the light-emitting diode illuminates the photodiode. The presence of media in the path is detected when this beam is interrupted. If necessary, a row of two or more such pairs of diodes can be positioned across the transport path to detect the size, shape, or orientation of the media. The diodes are connected via cables to amplifier and detector circuitry on a separate printed circuit board. A problem with this scheme is that additional structure is needed to support the diodes above and below the media guides. This structure, and the above-mentioned interconnecting cables, tend to get in the way during maintenance. The cables moreover require connectors, which take up space and pose a reliability problem in that the cables may become accidentally loosened or detached. Furthermore, the complexity of the mounting and cabling adds to the cost of the detector. When more than one pair of diodes is employed, all these problems are multiplied. European Patent Application EP-A-0504997 places a light-emitting diode and phototransistor on the same side of the media transport path, and provides a light-reflecting element, specifically a prism, on the opposite side to reflect light emitted by the light-emitting diode back to the phototransistor. By adding a third element (the prism), this scheme compounds the problems noted above. European Patent Application EP-A-0143188 uses optical fibres and light transmission cables to carry light from a light source to a position below the media transport path, receive the light at a position above the transport path, and carry the received light to an image sensor. This arrangement avoids the reliability problems of electrical connectors, but additional structure is still needed to support the optical fibres and cables, so the problems of extra space, extra cost, and inconvenience during maintenance still remain. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to simplify the structure of a media detector. Another object is to increase the reliability of a media detector. Yet another object is to simplify maintenance of a media detector and the machine in which it is used. Still another object is to reduce the cost of a media detector. The media detector according to the present invention comprises a light-emitting element, a light-sensing element, and a pair of media guides formed as plates backed by ribs. Light is emitted from the light-emitting element into a rib of the first media guide, this rib functioning as a first-light guide. The light is reflected within the first light guide, crosses the media transport path between the two media guides, and is reflected within a rib of the second media guide, this rib functioning as a second light guide. The light exits from the second light guide to the light-sensing element. The light-emitting and light-sensing elements are preferably mounted, together with their associated electronic circuitry, on a printed circuit board disposed adjacent the two media guides. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a first embodiment of the media detector according to the present invention ; Figure 2 is a sectional view along line X-X' in Figure 1; Figure 3 is a sectional view along line X-X" in Figure 1; Figure 4 is a sectional view along line S-S' in Figure 2; Figure 5 is a sectional view along line T-T' in Figure 2; Figure 6 is a perspective view of a second embodiment of the media detector according to the present invention ; Figure 7 is a sectional view along line Y-Y' in Figure 6; Figure 8 is a sectional view along line Y-Y" in Figure 6; Figure 9 is a sectional view along line S-S' in Figure 7; Figure 10 is a sectional view along line T-T' in Figure 7; Figure 11 is a sectional view illustrating a variation of the media detector according to the present invention. DETAILED DESCRIPTION OF THE INVENTION Embodiments of the invention will be described with reference to the attached drawings. These drawings illustrate the invention but do not restrict its scope, which should be determined solely from the appended claims. In the first embodiment, shown in FIG. 1, flat media 1 such as paper currency are transported by rollers or other means (not shown) through a transport path between an upper media guide 2 and lower media guide 3. The upper and lower media guides 2 and 3 are made of a material such as plastic and have the general form of flat plates backed by ribs. They are separated by a suitable gap permitting easy transport of the media 1 between them. Projecting from one side of the upper media guide 2 are a pair of entry ports 4a and 4b, for receiving light from a pair of light-emitting elements 5a and 5b such a light-emitting diodes. The light-emitting elements 5a and 5b are mounted, e.g. by soldering, on a printed circuit board 11, facing entry ports 4a and 4b. A pair of light-sensing elements 6a and 6b such as photodiodes are also mounted on the printed circuit board 11, facing exit ports (described later) in the lower media guide 3. The printed circuit board 11 is equipped with amplifier circuits for light-emitting elements 5a and 5b and detector circuits for light-sensing elements 6a and 6b. Entry ports 4a and 4b are the ends of a pair of light guides 7a and 7b which are integrated into ribs of the upper media guide 2. Entry ports 4a and 4b and light guides 7a and 7b are made of a transparent material, such as a clear plastic material. The other parts of the upper media guide 2 need not be transparent, but it is simplest if the entire media guide 2 is made of the same transparent material. Light guides 7a and 7b terminate in respective forty-five-degree reflectors 8a and 8b comprising, for example, reflective coatings on beveled ends of light paths 7a and 7b. Entry port 4a, light guide 7a, and reflector 8a are aligned on line X-X', perpendicular to the direction of travel of the media 1. Light guide 7b is bent as indicated by line X-X" so that reflector 8b is also disposed on line X-X'. Referring to FIG. 2, which is a sectional view through line X-X' in FIG. 1. the lower media guide 3 has a pair of light guides 9a and 9b, similar to light guides 7a and 7b, which terminate in a pair of reflectors 10a and 10b, similar to reflectors 8a and 8b. Light-sensing element 6a faces an exit port 12a at one end of light guide 9a. Exit port 12a is similar to entry port 4a. Both have square, flat surfaces with height and width dimensions substantially equal to, or slightly larger than, the corresponding dimensions of light-emitting and light-sensing elements 5a and 6a. If light-emitting and light-sensing elements 5a and 6a are round, the height and width of entry and exit ports 4a and 12a should be substantially equal to the diameters of light-emitting and light-sensing elements 5a and 6a, or slightly larger. Light guides 7a and 9a have the same cross-sectional dimensions as entry and exit ports 4a and 12a. Referring to FIG. 3, which is a sectional view through bent line X-X" in FIG. 1, light guide 9b has an exit port 12b which faces light-sensing element 6b. Entry and exit ports 4b and 12b are similar to entry and exit ports 4a and 12a, with similar dimensional relationships. FIG. 4 is a plan sectional view of part of the upper media guide 2, through line S-S' in FIG. 2, showing the bent configuration of light guide 7b and the paths followed by light from light-emitting elements 5a and 5b to reflectors 8a and 8b. FIG. 5 is a plan sectional view of part of the lower media guide 3, through line T-T' in FIG. 2, showing the bent configuration of light guide 9b and the paths followed by light from reflectors 10a and 10b to light-sensing elements 6a and 6b. Internal reflection from the sides of light guides 7b in FIG. 4 and 9b in FIG. 5 directs light around the bends in these light guides. If necessary, the sides of light guides 7b and 9b may be coated with a reflective material to ensure internal reflection. Next the operation of the media detector will be described. From FIGs. 2, 4, and 5, it can be seen that light emitted from light-emitting element 5a enters at entry port 4a, travels through light guide 7a, is reflected by reflector 8a, crosses the media transport path (provided no media 1 is present), is reflected again by reflector 10a, travels through light guide 9a, and exits at exit port 12a to light-sensing element 6a. Similarly, FIGs. 3, 4, and 5 show how light emitted from light-emitting element 5b enters at entry port 4b, travels through light guide 7b, is reflected by reflector 8b, crosses the media transport path (again provided no media 1 is present), is reflected a second time by reflector 10b, travels through light guide 9b, and exits at exit port 12b to light-sensing element 6b. Light-sensing elements 6a and 6b convert the incoming light to electrical signals for output to the detector circuits on the printed circuit board 11. When media 1 are inserted in the position shown in FIG. 1 and move along the transport path between the upper and lower media guides 2 and 3, if the media orientation is correct, the leading edge of the media 1 will simultaneously break the two beams of light reflected from reflectors 8a and 8b, at which time the outputs of light-sensing elements 6a and 6b will simultaneously drop, and the detector circuitry on the printed circuit board 11 will recognize that media transport is proceeding normally. If the media orientation is crooked, one beam will be broken before the other. The detector circuitry on the printed circuit board 11 can recognize the crookedness from the resulting time difference between the output transitions of light-sensing elements 6a and 6b. Suitable action can then be taken, such as stopping or reversing the direction of media transport. Since light-emitting and light-sensing elements 5a, 5b, 6a, and 6b are mounted directly on the printed circuit board 11, these elements can be connected to their amplifier and detector circuits by printed wiring traces. No cables are required at all. Nor is any extra structure necessary for the support of elements 5a, 5b, 6a, and 6b. Compared with the prior art, in which light-emitting and light-receiving elements were mounted above and below guides 2 and 3, the invented media detector has a simpler and neater structure, which facilitates maintenance work. It is also more reliable, because there are no cables to become loosened, or connectors in which faulty electrical contacts might develop. The absence of cables, connectors, and supporting structures furthermore reduces the cost of the detector. The novel light guides 7a, 7b, 9a, and 9b and reflectors 8a, 8b, 10a, and 10b introduce little or no added cost or complexity because they are integrated into the upper and lower media guides 2 and 3. The invention is not restricted to two light-emitting elements 5a and 5b and two light-sensing elements 6a and 6b. If it is not necessary to detect the orientation of the media 1, a single light-emitting element 5a and light-sensing element 6a will suffice. If it is necessary to detect the size, position, or shape of the media 1, additional light-emitting and light-receiving elements can be provided, with light guides and reflectors disposed in the media guides so that the beams cross the media transport path in any desired pattern. For example, three or more beams can be directed across the transport path at equally-spaced points disposed in a straight line perpendicular to the direction of media travel. FIGs. 6 to 10 show a second embodiment of the invention, which has multiple light-receiving elements but only a single light-emitting element, resulting in further structural simplification. Parts of this embodiment that are similar to parts in FIGs. 1 to 5 are labeled with the same reference numerals. In particular, the lower media guide 3 and its light guides 9a and 9b, reflectors 10a and 10b, exit ports 12a and 12b, and light-sensing elements 6a and 6b are identical to those in FIGs. 1 to 5. Referring to FIG. 6, light from a single light-emitting element 5 enters a light guide 7 in the upper media guide 2 at an entry port 4 and is guided to a reflector 8. Light guide 7 also has an intermediate partial reflector 13, in the form of a V-shaped notch with a reflective coating in the upper surface of light guide 7. To reflect half the light input at entry port 4, the notch should extend halfway through light guide 7. For correct reflection, the leading edge of reflector 13 (the left edge of the notch in the drawing) should be inclined at an angle of forty-five degrees to the top of light guide 7. Referring to FIG. 7, which is a sectional view through line Y-Y' in FIG. 6, light emitted by light-emitting element 5 is partially reflected at reflector 13. The light reflected by reflector 13 crosses the media transport path to reflector 10a in the lower media guide 3. The remaining light travels on to reflector 8, where it is reflected across the transport path to reflector 10b. The light reflected to reflector 10a returns as shown to light-sensing element 6a. Referring to FIG. 8, which is a sectional view along bent line Y-Y" in FIG. 6, the light reflected to reflector 10b travels through light guide 9b and exits at exit port 12b to light-sensing element 6b. FIG. 9 is a sectional plan view of part of the upper media guide 2 through line S-S' in FIG. 7, showing the single light-emitting element 5, entry port 4, light guide 7, and reflectors 8 and 13. FIG. 10 is a sectional plan view of part of the lower media guide 3 through line T-T' in FIG. 7, showing the same structure as in FIG. 5. The second embodiment operates in the same way as the first, but is even simpler in structure, more reliable, and less expensive, because it has only a single light-emitting element 5. FIG. 11 illustrates a variation of the second embodiment in which entry port 4 has a spherically concave surface instead of a flat surface, and exit ports 12a and 12b have spherically convex surfaces. The concave surface of entry port 4 enables more of the light emitted by light-emitting element 5 to be captured and directed through light guide 7 to reflectors 8 and 13. The convex surfaces of exit ports 12a and 12b act as lenses to concentrate the exiting light onto light-sensing elements 6a and 6b. (Light-sensing element 6b and exit port 12b are omitted from in FIG. 11.) These concave and convex surfaces result in a more efficient detector, requiring less electrical power. However, flat surfaces as in FIGs. 1 to 10 have the advantage of easier manufacturability. Concave and convex surfaces can also be employed for the entry ports 4a and 4b and exit ports 12a and 12b in the first embodiment in FIGs. 1 to 5, with the same advantages. To mention some other possible variations, the light-emitting and light-receiving elements need not be mounted directly on the printed circuit board 11. They may be mounted on, for example, the sides of the upper and lower media guides 2 and 3, or on members supporting media guides 2 and 3, and coupled to the printed circuit board 11 by short cables which will not interfere with maintenance. Reflective coatings may be omitted if adequate internal reflection is obtained without them. The roles of the upper and lower media guides 2 and 3 may be reversed, with the light-emitting elements facing the lower media guide 3 and the light-sensing elements facing the upper media guide 2. The transport path need not be horizontal; it may be vertical or have any other orientation. Those skilled in the art will recognize that still further modifications can be made without departing from the scope of the invention as claimed below.

Claims: A media detector for detecting the presence of media (1) travelling in a transport path formed as a gap between a first media guide (2) and a second media guide (3) which are positioned opposite and parallel to each other, having a light-emitting element (5a) for emitting light, a first light guide (7a) with an entry port (4a) receiving said light, for guiding said light to a point on one side of said transport path and directing said light across said transport path, a second light guide (9a) with an exit port (12a), for receiving said light at an opposite point on the other side of said transport path and guiding the light to said exit port (12a), and a light-sensing element (6a) for receiving the light from said exit port (12a) and converting the light to an electrical signal indicating the presence or absence of said media, characterised in that:- said first media guide (2) is formed as a plate backed by ribs; at least one of the ribs of said first media guide (2) functions as said first light guide (7a); said first light guide (7a) has a first reflector (8a) for reflecting said light across said transport path, said first light guide (7a) guiding said light from said entry port (4a) to said first reflector (8a); said second media guide (3) is formed as a plate backed by ribs; at least one of the ribs of said second media guide (3) functions as said second light guide (9a); said second light guide (9a) has a second reflector (10a) for receiving and reflecting the light reflected across said transport path from said first reflector (8a), said second light guide (9a) guiding said light from said second reflector (10a) to said exit port (12a); and said first reflector and said second reflector are positioned facing each other across said transport path. The detector of claim 1, wherein said entry port (4a) has a flat surface. The detector of claim 1, wherein said entry port (4a) has a concave surface for capturing the light emitted from said light-emitting element (5a). The detector of claim 1, wherein said entry port (4a) has width and height dimensions at least equal to corresponding dimensions of said light-emitting element (5a). The detector of claim 1, wherein said exit port (12a) has a flat surface. The detector of claim 1, wherein said exit port (12a) has a convex surface for concentrating said light onto said light-sensing element (6a). The detector of claim 1, wherein said exit port (12a) has width and height dimensions at least equal to corresponding dimensions of said light-sensing element (6a). The detector of claim 1, comprising a printed circuit board (11) on which said light-emitting element (5a) and said light-sensing element (6a) are mounted, said printed circuit board (11) having electronic circuitry to which said light-emitting element (5a) and said light-sensing element (6a) are coupled by printed wiring traces. The detector of claim 1, comprising a plurality of light-emitting elements (5a, 5b) and a like plurality of light-sensing elements (6a,6b), wherein: said first media guide (2) has ribs forming a like plurality of first light guides (7a, 7b) with respective entry ports (4a, 4b) and first reflectors (8a, 8b), said entry ports (4a, 4b) facing respective light-emitting elements (5a, 5b) for entry of light therefrom; and said second media guide (3) has ribs forming a like plurality of second light guides (9a, 9b) with respective exit ports (12a, 12b) and second reflectors (IOa, IOb), said second reflectors (IOa, IOb) facing respective first reflectors (8a, 8b) in said first media guide (2), and said exit ports (12a, 12b) facing respective light-sensing elements (6a, 6b) for exit of light thereto. The detector of claim 9 wherein said plurality of first reflectors (8a, 8b) are disposed in a straight line perpendicular to a direction of travel of said media (1) in said transport path. The detector of claim 1, comprising a single light-emitting element (5) and a plurality of light-sensing elements (6a, 6b), wherein: said first light guide (7) has a plurality of first reflectors (13, 8) for reflecting said light across said transport path; and said second media guide (3) has ribs forming a like plurality of second light guides (9a, 9b) with respective exit ports (12a, 12b) and second reflectors (lOa, lOb), said second reflectors (lOa, lOb) being disposed to receive light reflected from respective first reflectors (13, 8), and said exit ports (12a, 12b) facing respective light-sensing elements (6a, 6b) for exit of light thereto. The detector of claim 11, wherein at least one of said first reflectors (13) comprises a V-shaped notch formed at an intermediate position in said first light guide (7), for reflecting part of the light guided in said first light guide (7). The detector of claim 11, wherein said first light guide (7) extends in a straight line perpendicular to a direction of travel of said media (1) in said transport path. The detector of claim 13, wherein said second reflectors (10a,10b) are disposed at regular intervals in a straight line parallel to said first light guide (7). A method of detecting media transported in a transport path formed by a first media guide (2) formed as a plate backed by ribs and a second media guide (3) also formed as a plate backed by ribs, said first media guide and said second media guide being positioned opposite and parallel to each other, comprising the steps of: emitting light from a light-emitting element (5a) into a first rib of said first media guide (2), said first rib functioning as a first light guide; reflecting said light within said first light guide (7a) so as to direct said light across said transport path within a second light guide (9a) formed by a second rib of said second media guide (3), so that said light travels along said second light guide (9a) and exits from said second light guide (9a); and receiving the light that exits from said second light guide (9a) with a light-sensing element (6a), thereby converting said light to an electrical signal indicating the presence or absence of said media. The method of claim 15, wherein said second media guide (3) has ribs forming a plurality of second light guides (9a,9b), and said light is reflected at a plurality of points within said first light guide (7a), crosses said transport path at a like plurality of points, is reflected within said second light guides (9a,9b) at a corresponding plurality of points, and exits from said second light guides (9a,9b) to a corresponding plurality of light-sensing elements (6a,6b). The method of claim 16, wherein said light is emitted from a corresponding plurality of light-emitting elements (5a, 5b). The method of claim 16, wherein said light is emitted from a single light-emitting element (5). The method of claim 18, comprising the step of partially reflecting said light by at least one intermediate reflector (13) in said first light guide (7).

Inventors: GOTO MASAO C O OKI ELECTRIC IN, GOTO, MASAO, C/O OKI ELECTRIC IND. CO., LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1994
Main classification: G01B11
IPC codes: G01B11, B65H7, G07D9